The objective of this proposal is to develop solid membranes for the purposes of separating mixtures of gases and for the transport of metal ions. The proposal extends and builds on research the PI has been undertaking in this area over the past several years, and which has been funded by two NSF grants (CBT-8611646 (1986-1989) and CTS-8912634 (1989-1992)). The most recent grant (CTS-8912634) examined two processes, a separation of ammonia from hydrogen and nitrogen, and a separation of copper ion from iron and nickel. The first process was not successful, but high selectivity was obtained for the separation of ammonia from hydrogen and nitrogen by using a polyvinylammonium thiocyanate membrane. In a set of careful experiments, the PI demonstrated that the mechanism for this selectivity is the reaction of ammonia with the thiocyanate moiety attached to the polymer backbone. This reaction produces ammonium thiocyanate, a salt in which ammonia is very soluble. Additional ammonia then dissolves in the salt, and diffuses across this membrane through the salt. Unfortunately, the selectivity decreases as the temperature increases (presumably because of the lower solubility of ammonia in the salt), and these membranes are not useful at the high temperatures of industrial interest in ammonia synthesis. The proposal suggests two studies. The first is again an ammonia separation. The PI has begun to investigate persulfonic acid membranes. He has found that these retain a sixty to one selectivity of ammonia to nitrogen at the high temperatures of relevance to ammonia synthesis. The new proposal suggests characterizing the selectivity of these membranes in more detail, and identifying the mechanism of selectivity. The second study is concerned with developing membranes for the selective and rapid transport of lithium ion. Such membranes can play a crucial role in the design of a rechargeable lithium battery.
